CO2 absorption processes using aqueous amine solutions facilitate the removal of CO2 from gas streams in many industries. A common process is known as wet chemical stripping where one or more reversible chemical reactions between CO2 and amine substances produce liquid species, such as a carbamate. The conversion of carbamate back to CO2 proceeds through a thermal regeneration process, typically at a temperature of about 120° C. As a result, the process is energy intensive. Additionally, the amine solution has a limited lifetime due to amine oxidation, and amine solutions may exacerbate corrosion problems of associated process equipment.
To mitigate these issues, solid sorbents serve as alternatives to wet chemical stripping via the formation of carbamate species. Important considerations include the ability to regenerate an absorbent and the ease of its regeneration, and multiple solid CO2 sorbents exist. Efforts have been made to reversibly adsorb CO2 on silica gel modified with amine. See U.S. Pat. No. 5,087,597 to Leal et al., issued Feb. 11, 1992. Methods have also been disclosed for incorporating liquid amines onto the surface of support substrates having relatively high surface areas. See U.S. Pat. Nos. 5,876,488 and 5,492,683 to Birbara et al., issued Mar. 2, 1999 and Feb. 20, 1996 respectively, and see U.S. Pat. No. 4,810,266 to Zinnen et al., issued Mar. 7, 1989. Amines have also been distributed within the interlayers of clay substrates. See U.S. Pat. No. 6,908,497 to Siriwardane, issued Jun. 21, 2005.
The effective lifetime of these solid sorbents is impacted by amine oxidation in environments where the oxygen concentration is substantial. The Interaction of amine with oxygen is known to degrade the amines. See e.g., Lepaumier et al., “New Amines for CO2 Capture. II. Oxidative Degradation Mechanisms,” Industrial & Engineering Chemistry Research 48(20) (2009), among others.
Since air contains 21% oxygen, air degradation is a significant concern. Correspondingly, it would be advantageous to provide a method for producing a solid sorbent offering increased resistance to oxygen degradation over those currently offered. Additionally, since the degradation mechanism with oxygen is reported to have acidic intermediates, it would be advantageous to provide a method by which the acidic intermediate formation could be minimized through inclusion of a relatively inexpensive material, such as an alkali.
Disclosed here is a method for the production of a clay-alkali-amine CO2 sorbent exhibiting an increased effective lifetime in environments having substantial oxygen concentrations. The method generates the clay-alkali-amine CO2 sorbent through integration of a clay substrate, a basic alkali salt, and an amine liquid. The clay substrate serves as a plurality of internally situated reaction sites while the basic alkali salt acts as a strong base to generate a high pH environment. The basic alkali salt greatly mitigates oxygen degradation of the amine and significantly prolongs the useful life of the clay-alkali-amine CO2 sorbent. The clay-alkali-amine CO2 sorbent produced is particularly effective for low temperature CO2 removal cycles from air/CO2 having a CO2 concentration less than around 1% and an oxygen concentration around 21%.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.